Heating body

ABSTRACT

This heating body is cut from a metal sheet (1) and defined by slots (2) obtained by punch stamping on a support (4) of plastics foam. The opposite edges of these slots (2) are spaced from one another by deformation of the portion of the conductor (7) adjacent to these slots, obtained by the bevelled shape of the portion of the cutter (3) defining the cutting edge and by the compressibility of the material forming the support (4). According to the method of manufacturing this heating body, its external profile and the slots (2) are obtained by a same single punching operation.

CROSS REFERENCE TO RELATED APPLICATION

This application is a national phase of PCT/CH81/00125 filed Nov. 10,1981 and based upon the European international application 81 81,064.4of Apr. 30, 1981 and Swiss application 8385/80.3 of Nov. 12, 1980.

The present invention relates to a heating body comprising a metal sheetassociated at least at one of its faces with an insulating support andhaving parallel slots extending alternately from two opposite edges ofthis sheet and terminating at a distance from the edge opposite to thatfrom which they extend in order to form a continuous resistive conductorover the entire surface of this sheet.

BACKGROUND OF THE INVENTION

It has already been proposed in Austrian Pat. No. 345 579, the BritishPat. No. 1,192,927 and U.S. Pat. No. 3,214,565 in particular, to form aheating body from a metal sheet by providing a conductor having asubstantially constant section as a result of parallel slots extendingalternately from two opposite edges of this sheet and terminating at acertain distance from the edge opposite to that from which they extendin order to distribute the heating current over the entire surface ofthe metal sheet in a substantially uniform manner. These slots areobtained in a machining operation during which material from the metalsheet is removed over a certain width in particular by milling orsawing, in order to ensure the desired current distribution.

The manufacture of a heating body of this type requires, in particularif the metal sheet is thin, the initial fastening of this sheet to asupport before the slots are cut by milling or sawing. The main drawbackof the solutions proposed up to now is that the cutting of the slotsrequires a removal of material in order to provide a spacing between theedges of these slots thus involving a machining operation which isrelatively slow and therefore badly adapted to the low cost productionof a mass produced article.

It has also been proposed in the European Patent EP 0 004 829 toassociate a heating body with a foam of a thermo-formable material so asto be able to mold this foam, from which a blank designed to provide anaccurate fit between a piece of clothing or an accessory and a part ofthe human body has in the first instance been produced. This fit isobtained by moulding this blank, heated by the heating body which isincorporated therein, to the exact dimensions of this part of the humanbody.

This heating body is constructed using printed circuit techniques.Although this technique is completely suited to the nature of theplastic foam support, to the extent in which it enables the separateproduction of the heating body and its combination with the foamsupport, this involves a technology reserved for the manufacture ofelectrical circuits. The cost of manufacture of these circuits isdisproportionate when this technology is only used to provide simpleheating bodies designed for mass produced articles since a heating bodyof this type does not require the accuracy of printed circuits.

In addition it has already been proposed in the Swiss Pat. No. 421 330to provide a heating body of the type mentioned above by stamping of athin metal sheet glued to an insulating support. It should however benoted that a method of manufacture of this type gives rise toconsiderable practical difficulties, given that when the metal sheet andthe insulating coating are cut, the sheet and the coating aretransformed into a thin zigzag shaped strip such that the geometry ofthe sheet no longer exists in the absence of a support, which leads toproblems in the manufacture, handling and use of the heating body.

OBJECT OF THE INVENTION

The object of the invention is to remedy, at least partially, thedrawbacks of the above-mentioned solutions.

SUMMARY OF THE INVENTION

For this purpose, the invention firstly relates to a heating bodycomprising a metal sheet associated by at least one of its faces with aninsulating support and having parallel slots extending alternately fromtwo opposite edges of this sheet and terminating at a distance from theedge opposite to that from which they extend in order to form acontinuous resistive conductor over the entire surface of this sheet,this conductor being designed to be connected to a current source atboth its ends, the slots being provided by punch cutting and theiropposite edges being spaced from one another by deformation of theconductor portion adjacent to at least one of the edges of these slots.This heating body is characterised in that the said slots only at mosttraverse the said support over a portion of their length in order toconnect together in a lateral manner the parallel portions of the saidconductor.

The invention also relates to a method of manufacturing this heatingbody characterised in that both the cutting of the peripheral edge ofthis heating body and its support and the cutting of the slots designedto define the said conductor are obtained by means of a single stampingoperation.

The invention lastly relates to a use of this heating body associatedwith at least one layer of thermo-formable foam in order to match twonon-complementary surfaces to one another by compression and thenheating of the said foam to the thermo-forming temperature between thesaid non-complementary surfaces.

The main advantage of the invention lies in the fact that, once cut, theparallel edges of the resistive conductor remain laterally connected toeach other by virtue of the fact that the support on which the metalsheet is cut, after having been glued, is not completely cut or at leastnot cut over the entire length of the slot. The heating body obtainedtherefore retains, after cutting, its geometrical cohesion and maytherefore be obtained from a single cutting operation of a sheetmaterial formed by the metal sheet and its support which are fixedtogether.

BRIEF DESCRIPTION OF THE DRAWING

The attached drawing shows in diagram form and by way of example, anembodiment and variants of the heating body of the present invention:

FIG. 1 is a perspective view of this embodiment,

FIG. 2 is a perspective view of a cutting tool for this heating body,

FIG. 3 is a view in section along the line II--II of FIG. 1,

FIG. 4 is a perspective view illustrating the manufacture of a heatingbody associated with a sole of thermo-formable material,

FIG. 5 is a perspective view of a further manufacturing stage of thissole,

FIG. 6 is a view of a heated vacuum flask with some components removed,

FIG. 7 is a plan view from the side of the support of a further variantof the invention,

FIG. 8 is an enlarged view in cross-section along the line VIII--VIII ofFIG. 7 during the cutting operation, and

FIG. 9 is a cross-section showing a use of the heating body for matchingtwo non-complementary surfaces to one another.

SPECIFIC DESCRIPTION

The heating body shown in FIGS. 1 and 3 is constituted by a metal sheet1, for example an aluminum sheet having a thickness of approximately0.05 mm,in which the slots 2 are punched out by means of a cutter 3provided with blades 3a.

For this purpose, the metal sheet 1 is disposed on a cutting support 4madeof an elastically compressible material such as a sheet of plasticfoam designed to enable the blades 3a of the cutter 3 to pass throughthe metalsheet 1. This support 4 is itself located on the block of astamping press (not shown). The metal sheet 1 is preferably fixed to thesupport 4 by adhesive. Consequently this solution is particularlysuitable when the heating body constructed in this way is designed toheat foam of a thermo-formable type such as a polyethylene foam, asdescribed for examplein the European Patent Application No. 0 004 829.

In the embodiment shown in FIG. 1, the slots 2 are parallel and extendalternately from two opposite edges 1a, 1b of the metal sheet 1 butterminate at a certain distance from the other edge, thus forming acontinuous electrical conductor 7 constituting a heating body ofsubstantially constant section between two terminals 5 and 6 connectedto an electrical current source S.

As can be seen in particular from FIG. 3, the opposite edges of theslots 2are spaced from one another, this spacing being obtained bydeformation of the portion of the resistive conductor adjacent to theedges of this slot 2 such that these edges project from the plane of themetal sheet on the side of the sheet adjacent to the support 4. Thisdeformation is obtained during the cutting operation and is a functionof the pressure required tocause the tool to penetrate into the metalsheet 1 and the compression resistance of the cutting support 4. Thepressure of penetration of the cutter 3 is a function of the thicknessand the nature of the material used for the metal sheet 1 and the shapeof the cutting edge of the cutter, as will be explained in more detailbelow. The deformation of the edges of the slot may therefore be of asufficient size to separate and isolate in an electrical manner from oneanother the adjacent portions of the resistive conductor 7 withoutrequiring any removal of material. With the two edges of the slot 2spaced in this way, the portions of the resistive electrical conductoradjacent to this slot are therefore insulated from one another thusforcing the current to pass through the resistive conductor 7 over itsentire length and thus to heat, by Joule effect, the entire surface ofthe metal sheet.

In order to facilitate the cutting of the metal sheet 1 and concentratetheinitial pressure of the blades 3a of the cutter 3 on very smallsurfaces thus increasing the penetration capacity of these blades 3a,the cutting edge of these blades may be scalloped. In addition, inparticular when thesupport 4 is designed to remain fixed to the metalsheet 1 once the latter has been cut, the formation of scallops alongthe cutting edge of the blade 3a enables material bridges to be left inthe support 4 between the points of the scallops such that the edges ofthe slots cut in this support 4 are not separated. The support thereforeretains its geometry and consequently that of the conductor cut from themetal sheet 1. This enables the subsequent handling and use of theheating body whose paralleledges remain connected laterally to oneanother by means of the support, asshown in FIG. 3, as the rear face ofthe support 4 does not have a cut section or possibly only has a cutsection at the location of the points of the blade 3a. Tests carried outwith straight blades which only passed through approximately half thethickness of the support over the entire length of the slot, alsoenabled good results to be obtained.

The spacing provided between the edges of the slots 2 may be increasedby using a blade 3a of a cutter 3 having one face, adjacent to thecutting edge, forming a bevel with the plane of the blade, as shown inFIG. 2, in order to enable further deformation of the edge of the sloton the side ofthe bevel of this blade.

Amongst the advantages of this heating body and its method ofmanufacture, it should be noted that the periphery of the body may becut, during the same cutting operation as for the slots, from acomposite sheet material 8(FIG. 4) formed from a sheet 8a of elasticallycompressible plastic foam onwhich a sheet of aluminium 8b is attached byadhesive. In this example, theheating bodies are cut into the shape ofsoles in order to dispose each body 9a with its underlying foam layer 9bon a sole blank of thermo-formable plastic foam (not shown), such as alow density, nitrogen blown polyethylene foam, in order to obtain athermo-formable sole with incorporated heating designed to be locatedwithin a shoe in order to match this shoe very accurately to the foot ofthe wearer by molding of the sole. Tests carried out showed that thethermo-forming temperature of "low density" polyethylene foams, i.e.approximately 140° C., was well tolerated and did not cause any burningof the skin.

FIG. 4 again shows the distribution of the slots 10 which may be used inthe case of a heating body of this type. In the application in question,it may be that the spacing between the edges of the slots 10 is stillinsufficient, in particular when the heating body is subject to strongcompression during use, as may be the case with a heated sole. It isthen envisaged to space the slots 10 after they have been cut forexample by bending the cut foam sheet 9b and the heating body 9a presenton the convex face of this foam sheet 9b by passing it about a cylinder11 (FIG. 5) and by introducing into these spaced slots an insulatingsubstance which may, for example, be in a liquid, solid or gaseous form.In this wayit is possible, for example, to coat the edges of the slot 10with an insulating lacquer or a like product, preventing the edges ofthe slot 10 from coming into contact, by passing the heating body 9athrough a bath B containing the liquid insulating substance. As avariant it is also be possible to introduce a solid insulating gasketinto this slot.

As mentioned above, the heating body is preferably glued to a support ofelectrical insulating material such that, when cut, the adjacentportions of the resistive conductor formed in this way remain connectedby means ofthe support material so that the heating body may be readilyhandled.

For this purpose, the metal sheet may be glued to a layer of plasticfoam by a rubber-based adhesive which decomposes at a temperature ofapproximately 90° C. When the heating body has been cut, it then has itsfree face glued to a further receiver surface on which it is designed tobe permanently fixed by means of a thermosetting resin, for example anepoxy resin. When the free face of the heating body has been applied tothis adhesive-bearing receiver surface, the heating body is connected toa current source in order to raise its temperature to approximately 100°C. such that the rubber-based adhesive decomposes. It is then possibleto remove the foam which has acted as a support during cutting, theheating body remaining fixed to this surface by the hardened epoxyresin.

FIG. 6 illustrates the application of the invention to the manufactureof avacuum flask in which the heating body 12 is cut on a layer of foam13 which is relatively thin and dense and is a good conductor of heatsuch asa neoprene foam on which it is glued. When the heating body hasbeen cut, the free face of the foam layer 13 is then glued around aflask 14. As theslots 15 of the heating body are orientated along thegeneratrices of the flask, the edges of these slots are spaced. Theheating body 12 is then covered with a layer of a covering insulatingfoam 16.

It is also possible to envisage cutting the slots by means of a cutterhaving two symmetrical bevels on either side of the cutting edge thusproducing an identical deformation of the portions of the resistiveconductor adjacent to the opposite edges of this slot.

In the case of use of the heating body of the invention to obtain thethermo-forming of a foam layer in order to match two non-complementarysurfaces to one another as shown in FIG. 9, when the support of theheating body is constituted by the thermoplastic foam itself, at themoment of thermo-forming, when the foam is at its flow temperature, theheating body is no longer mechanically reinforced and is then requiredto support all the stresses. As this heating body is generally made of asheet of aluminium having a thickness of approximately 0.05 mm, it isnot unusual for these stresses to exceed the tensile strength limitssuch thatthe heating body is no longer usable. It is for this reasonthat, in accordance with a variant of the present invention (FIGS. 7, 8and 9) a metal sheet 17 is fixed to a support 18 of a nonthermo-formable material,such as paper, cardboard or synthetic felt. Inorder that the support has asuitable mechanical strength during thethermo-forming operation of the layer(s) of foam 19 provided on one orboth sides of the metal sheet 17 and its support 18, the material of thesupport, in particular of cardboard or felt, should advantageously be ofa stiffness such that, in certain cases, it opposes the local crushingof the foam between the two non-complementary surfaces and tends todistribute the pressure over a larger surface area than that of thesurface irregularity causing the local crushing of the foam. This takesplace when one of the surfaces to be adapted has, for example, aclose-set sequence of convex and concave portions which the support isunable to fit as a result of its stiffness.

In order to remedy this drawback, the material of the support 18 mayhave passing through it slots 20 provided along slots 20a of the metalsheet 17but terminating at a certain distance from the two oppositeedges of the support. The parallel slots passing through this supportform tongues 21 attached at their two ends to the opposite edges of thissupport. While retaining the geometry of the support, these tongues 21enable a large degree of flexibility of adaptation as a result of thefact that two adjacent tongues may be displaced in two oppositedirections and may even be slightly spaced from one another in theirmedian portion. In addition these slots considerably increase theflexibility of the support 18. In the case of a thermo-formable sole forexample, the tongues 21 which are provided transversely increase theflexibility of the sole in the longitudinal direction thereby increasingcomfort. By means of these tongues, it is therefore possible toreconcile the mechanical strengthening of the conductor portionsresulting from the cutting of the metal sheet 17 with the flexibility ofthe support, which is of great importance when it is required to matchtwo non-complementary surfaces by the thermo-forming of a foam layerwhich has previously been compressed inorder to enable a local crushingof this layer as a function of the irregularities between the twosurfaces to be matched.

It should be noted that the width of the tongues 21 is not necessarilyidentical to that of the parallel portions of the resistive conductorcut from the metal sheet 17, but may correspond to any multiple of thiswidth.In the case of a metal sheet 17 having one face only associatedwith a support 18, the cutting of the resistive conductor and the slots20 passing through the support may be carried out in a single operationusinga cutter 22 having a non-scalloped blade which has two projectingedges 22aand by controlling its penetration such that the portion of theblade 22b following this projecting edge only partially passes throughthe thicknessof the support 18 such that only the metal sheet 17 is cutfacing this portion 22b of the cutter.

If, however, a support 18 extends along both sides of the metal sheet,as shown in FIG. 9, one of these two supports must be cut separately andthenadded to the free side of the metal sheet 17 associated with theother support. As the external contour of the heating body and theparallel slots forming the conductor are preferably simultaneouslypunched out, in accordance with the method of production illustrated anddescribed with respect to FIG. 4, and in that both the support 18associated with the metal sheet 17 and the other single support are cutwith the same tool, itis sufficient to line up the respective edges ofthe two supports for theirslots to coincide as well. FIG. 9 also showsthe case in which the heating body formed from the metal sheet 17, heldbetween two support layers 18, receives two thicknesses 19 of foam of athermo-formable material designedto match the two surfaces 23, 24 whichare non-complementary, by compression of these surfaces andthermo-forming of the foam thicknesses 23 by means of the heating body17.

We claim:
 1. A heating body comprising a metal sheet attached by atleast one of its faces to a surface of an insulating support and havingparallel slots extending alternately from two opposite edges of thissheet and terminating at a distance from the edge opposite to that fromwhich they start in order to form a resistive conductor over the entiresurface of the sheet, designed to be connected to a current source atopposite ends, these slots being provided by punching and being spacedfrom one another by deformation of the portion of the conductor adjacentto at least one of the said edges of these slots into the surface of thesupport, said slots passing through the said support only, at the most,over a portion of their length in order to laterally connect theparallel portions of the said conductor mechanically to one another atboth ends of each slot while providing electrical interconnection ofadjacent parallel portions only at one end of each slot.
 2. The heatingbody defined in claim 1 wherein said slots pass through the said supportperpendicular to at least one portion of the slots passing through thesaid sheet, while terminating at a distance from the opposite edges ofthis support, in order to form adjacent laminations attached by theirtwo ends to the marginal portions of this support.
 3. The heating bodydefined in claim 1 or 2 wherein said support is of a non-thermo-formableflexible material.
 4. The heating body defined in claim 1 wherein thesaid slots do not pass through the said support at least over the majorportion of their length.